Dental articulator trays

ABSTRACT

Improved dental articulators of either the pivotal or stem type are provided with a tray permanently attached to each of the two articulator platforms, and each tray has a keyway slot of dovetail cross section extending longitudinally along its inner or operating face as a coupling means for engaging a mounting base bearing a dental cast on one side and a corresponding dovetail key on the other side for engaging said slot. The key and keyway taper to a substantial extent in the horizontal plane as they approach a pivot or stem at the back of the articulator, and they taper at least slightly in the vertical plane in the same direction to provide a coupling system that can be easily and rapidly engaged or disengaged and yet locate the mounting base in any similarly equipped articulator with great precision. Also, a novel method of constructing this articulator involves assembling preformed trays with their keyways engaging keys of two opposite faces of a mounting jig to maintain exact alignment of the trays and their keyways while the other sides of the trays are being permanently cemented to the platforms of the articulator.

United States Patent 1191 Spinella DENTAL ARTICULATOR TRAYS [76] Inventor: S. Charles Spinella, Mayberry Mansion Apt. Cl 18, 5200 N.E. 24th Ter., Fort Lauderdale, Fla. 33308 22 Filed: Dec. 1, 1972 21 Appl. No.: 311,104

Primary Examiner-Louis G. Mancene Assistant Examiner-J. Q. Lever I Attorney, Agent, or Firm-Morgan, Finnegan, Durham & Pine 1451 May 7,1974

[5 7] ABSTRACT Improved dental articulators of either the pivotal or stem type are provided with a tray permanently attached to each of the two articulator platforms, and each tray has a keyway slot of dovetail cross section extending longitudinally along its inner or operating face as a coupling means for engaging a mounting base bearing a dental cast on one side and a corresponding dovetail key on the other side for engaging said slot. The key and keyway taper to a substantial extent in the horizontal plane as they approach a pivot or stem at the back of 'the articulator, and they taper at least slightly in the vertical plane in the same direction to provide a coupling system that can be easily and rapidly engaged or disengaged and yet locate the mounting base in any similarly equipped articulator with great precision. Also, a novel method of constructing this articulator involves assembling preformed trays with their keyways engaging keys of two opposite faces of a mounting jig to maintain exact alignment of the trays and their keyways while the other sides of the trays are being permanently cementedto the platforms of the articulator.

15 Claims, 2 Drawing Figures agaoasas ATENTEU M 7 I974 SHEET 1 OF 2 PATENTEBMAY 1 m4 8;808;888

SHEET 2 0F 2 1 DENTAL ARTICULATOR TRAYS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention is concerned with improved dental articulators and their manufacture whereby they are equipped with a permanently attached tray of particu lar configuration on each platform. These trays are provided with coupling means for interlocking engagement with complementary coupling means on the mounting bases of dental casts for removably mounting the dental cast in the articulator with precision.

2. Prior Art In conventional practice for dental restorations, the dentist takes a wax bite of the patients teethafter suitable preparation and then makes plaster casts which are sent along with the wax bite or impression to the dental laboratory. The laboratory assembles the two casts and the wax bitetogether within the articulator frame to determine the height setting; then the whole articulator body is tilted back 90 without opening it, and a suitable cement (i.e. plaster of paris or dental stone, hereinafter termed plaster) is cast around each frame or platform of the articulator after said assembly has been properly aligned visually with the articulator axis. Meanwhile, the wax bite maintains the proper alignment between the casts of the upper and lower jaws of the patient. This casting operation cements the upper, jaw cast to the upper frame of the articulator by means of the plaster which embeds the upper frame or platform of the articulator; and the lower jaw east and lower frame are similarly bonded. After the plaster has hardened, the excess plaster is trimmed away, and the laboratory technician then opens the articulator and removes the wax bite before building the desired kind of dental restoration in conventional manner. I

This mounting of the dental casts in an articulator is of an irrernovable type, because those casts can only be removed from the articulator by breaking their mounting bases to free the framework of the articulator platform. Such removal is deferred until the dentist and patient accept the finished dental restoration. Meanwhile, the denture is delivered to the dentist by mail or otherwise while mounted on the articulator in order that the dentist may check the fit of the dental restoration and ascertain what if any corrections must be made in order to provide well fitting and serviceable dentures for the patient. If any alterations are required, the denture is mounted back on the dental cast in the articulator, and the entire articulatoris returned to the laboratory for further work. Thus, a separate articulator is required for each patient, and that articulator must be reserved exclusively for that patient until the dental restoration has been completed which may require several corrections or alterations. This can prevent the use of the articulator by any other patient for a period of weeks or even months in additionto sometimes involving substantial delivery charges for sending the fairly heavy aradjustable articulators provided with ball joints and set screws, and these have removable mounting bases for the dental casts; but it appears that the casts must be rearticulated or properly aligned whenever they are reinstalled, if that articulator has been employed in the interim for any other patient. Also, these articulators are relatively complex, and one of them requires casting special metal plates in the mounting base to provide a demountable unit.

Neer US. Pat. No. 2,61 1,961 describes a device designed for the exact repositioning .of dental casts wherein the lower jaw cast is mounted on a base and positioned thereon by a series of intersecting V grooves oriented in three different directions. Only the bottom mounting base is capable of quick registry when it is being remounted in that articulator; and even then the lower base is not locked in by the grooves but merely rests thereon, and it may be subject to misalignment by having its ribs ride somewhat upward along the sides of the grooves in the bottom platform. The upper jaw cast is mounted in conventional manner with an articulator platform embedded therein, and it differs from common constructions only in having an arm that is removable by detaching two machine screws.

Benfield et al. US. Pat. No. 2,911,722 is concerned with dental trays of rather complicated special designs equipped with internal serrations and special gates or latches. These devices permit the dental casts mounted on plaster bases to be removed for work outside of the dental tray and then reinstalled in the locking tray of the articulator in proper registration with its former position. v

Windish US. Pat. No. 3,059,336 discloses a stem articulator that is particularly designed to enable dental restorations to be provided without requiring the dentist to adjust the surfaces thereof in the patients mouth. In one embodiment, transverse or lateral undercut grooves of apparently constant size are provided so that the mounted casts may slide laterally and be removed. Alternatively, in a different embodiment, pins are employed to secure the mounted casts against movement.

- The present invention is directed at improved dental articulators which permit dental casts to be rapidly and easily removed and reinstalled on the trays of the dental articulator without loss of proper alignment of the upper and lower dental casts. It provides important economies in respect of the technicians time as well as in materials and equipment.

SUMMARY OF THE INVENTION The present invention relates to an improved dental articulator in which the improvement comprises trays that are rigidly attached to the articulator platforms and each tray being provided with an undercut coupling means which has tapering dimensions in two different planes with said dimensions tapering inthe direction of coupling engagement whereby said trays are capable of rapid and precise engagement with a com- 3 of a close sliding engagement with.the tray coupling means.

Another aspect of the invention involves the method of making these articulators including one or more of such features as uniting preformed trays with the structural members of an articulator while the trays are facing one another in predetermined parallel space relationship with their tapering, undercut coupling means disposed in mirror image alignment opposite one another. Preferably, this is accomplished by means of a mounting jig on which said articulator trays are assembled. Subsequently mounting bases may be cast for the dental casts while at the same time forming complementary coupling means on the other side of said mounting base by means of the coupling means on the dental trays serving as molds for the complementary coupling means that are being formed on the mounting bases. Various other objects, advantages and benefits of the invention will be apparent to those skilled in the art upon consideration of the detailed disclosure hereinafter.

DESCRIPTION OF THE DRAWINGS FIG. 1 is an exploded perspective view. illustrating the important parts and manner of construction of one embodiment of an articulator according to the present invention.

FIG. 2 is a front elevation of the completed articulator with a'lower jaw cast mounted therein.

DESCRIPTION OF SPECIFIC EMBODIMENTS In FIG. 1 is shown in schematic fashion an articulator frame of a conventional nonadjustable type that is commonly used in fixedly mounting dental casts by cementing them to the open frame structure of the articulator with plaster which embeds the upper and lower metal platforms 12 and 14, respectively. In the present embodiment, this articulator chassis is employed to carry the novel trays described in detail hereinafter. These trays allow the dental casts and their mounting bases to be readily mounted on and disengaged from the articulator. The other basic members of this simple hinged articulator consist of the rear frame members 16 connected to thelower platform 14 and projecting upwardly at the rear to provide journals 18 for the pivot pin 20 and the rear support arms 22 which connect the upper platform 12 to the pivot pin 20. An adjustable stop means (not shown) is usually provided to restrict the extent of the swing of the upper platform 12 towards the lower platform 14 in order to avoid any damage to dental casts or a dental restoration resulting from an accidental rapid downward swing of the upper platform 12. v

In the center of FIG. 1 are illustrated a lower dental tray 24 and an inverted upper tray 26 of the same construction which are ready to be aligned and permanently fastened to the articulator chassis 10 as described hereinafter. The tray 24 has an upwardly extending lip 28 at its rear edge, and a substantial area of its upper or operating face 30 is preferably flat and relatively smooth except for the coupling slot or keyway 32. As may be readily seen in FIG. 2, this slot 32 is of the undercut type, preferably of dovetail cross section, in order to provide an interlocking engagement with a mounting base as described hereinafter.

As will be evident to those skilled in the art, many other articulator frames, including those of the stem type as well as adjustable and nonadjustable pivoting types, may also be employed as'the chassis members of the present articulators. However, little is gained in'certain instances by using an adjustable articulator frame inasmuch as some of these employ complex construction features or involved procedures for realigning mounted casts after they have been removed from an articulator, consequently reinstallation is often relatively slow. In contrast, the new articulators are selfaligning and permit rapid engagement and release of mounted dental casts.

It will be observed that the keyway 32 is relatively wide at its open end 34 and that it tapers in width as it extends longitudinally toward the articulator axis or pivot pin 20 at the rear. Thus, the rear or inner end 36 of the slot, which is preferably but not necessarily closed, is distinctly narrower than its open end 34. The angle of taper between the two edges of the slot may vary widely and still provide a good coupling fit. Excellent results are obtainable with taper angles of about 8 to 20 degrees, but somewhat smaller angles and larger angles of or even more are also contemplated.

The depth of the slot 32 should also diminish and become shallower at its inner end 36 than at its outer end 34, but this draft or angle of taper may be much smaller and still provide free but precisecoupling engagement. For example, the angle of taper relative to the horizontal may be as little as about l, but a slope of about 2 or more is generally preferable.- However, it is only necessary to provide enough taper or draft in the tapering dimensions for easy separation of theinterlocked members. The tapering dimensions of the undercut coupling members of this invention provide important advantages in several respects. They avoid the sloppy fit that one is likely to encounter with a reasonably freely sliding fitbetween members having parallel sides; and they render engagement and disengagement of the mounting bases very easy while providing a high degree of precision. I

The outer or nonoperating face 38 is optionally provided with one or more grooves 40 of rectangular cross section for the purpose of enlarging the surface area of that face in contact with the adhesive described hereinafter.

The trays 24 and 26 may be made from a wide variety of .construction materials, in fact from almost any solid type that can be molded or machined to form trays of 5 ferred as they can be molded rapidly at low cost with good precision by injection molding techniques. This is generally preferable to shaping thermosetting resins by compression molding or casting a tray from molten metal or machining it from a metal bar.

Among the many suitable thermoplastic resins are the polyolefins, such as polyethylene and polypropylene, acrylic polymers as exemplified by polymethylmethacrylate, nylons, formaldehyde polymers as illustrated by DELRIN, polyphenyloxide, polycarbonates like LEXAN, acrylonitrile-butadiene-styrene (ABS) resins, acetal copolymer resins, suchas CELCON, polyethylene terephthalate, polystyrene, vinyl resins as illustrated by the polymers of vinyl chloride and its copolymers with vinyl acetate, ABS resins, etc. In general a dimensionally stable and tough resin of high impact characteristics is preferred for providing a long service life for the trays.

FIG. 1 also depicts a mounting jig 42 as a rectangular block bearing a male coupling member in theform of an undercut key 44 on its upper side and asimilar key 46 on its lower side. These keys are of dovetail cross section and they taper from a wide end 48 to a narrow end 50; they are complementary to the keyways 32 and thus designed to fit closely into those ksyways in the in the upper tray. The lower cast 58 is mounted on the trays 24 and 26. This jig is intended to establish the proper alignment of the trays while the articulators of the present invention are being constructed.

In assembling the articulators, the tray 24 is placed against the bottom face of the jig 42 and pushed into upper tray 26 is similarly fastened in place by the resin layer 54 which embeds the upper platform 12. It will be apparent that the keyways 32 are sharply undercut at their comers 56 in a dovetail-shaped cross section to provide interlocking engagement with the keys on the mounting bases described hereinafter. In general, a dovetail configuration is preferred for simplicity, and the undercut angle relative to the horizontal surface of the tray is desirably between about 30 and 60, e.g., about The undercut angle may be considerably greater or less than this range, but little or no advantage is gained thereby as extreme angular cuts tend to make the master mold for the trays more difficult and expensive to fabricate. Other-undercut configurations may also be employed, as exemplified by a coupling key system of T-shape with square or rounded ends on the crossbar of the T.

FIG. 2 also illustrates the position in the device of a dental casting 58 of the lower jaw. The upper jaw casting is usually articulated at the same time but has been omitted here in order to illustrate the tapered keyway plaster base 60 which has a projecting key 62 engaging the keyway 32 of the lower tray 24. The key 62 is tapered both in width and depth in the same way as the keyway slot 32; hence this key is complementary andfonns a close interlocking fit with the keyway 32.

place with its dovetail slot 32 engaging the key 46 until a snug interlocked fit is obtained; and the upper tray 26 is similarly fitted onto the projecting key 44 at the top of the jig block 42. This orients the two trays in a precise manner with their keyways 32 in mirror image alignment and the inner or operating faces of the trays 24 and 26 parallel to one another and spaced apart by the depth of the side walls of jig 42, a spacing that corresponds to the typical 3.75 4.0 inches opening of a conventional articulator. A liquid or paste resin adhesive is spread onto the outer faces 38 and grooves 40 of trays 24 and 26, then the assembly onthe jig is inserted between the two metal frame platforms l2 and 14 and more of the adhesive is disposed in and around those frame members 12 and 14 to completely cover them. Next the adhesive is allowed to set and permanently bond the tray 26 to the platform 12 and'the tray 24 to the platform 14. Other means of fixedly mounting these trays, including screws and bolts, are contemplated but are usually less desirable as such construction may be less rigid and/or more expensive.

Suitable resins for this luting or cementing operation are known liquid or a semisolid resin compositions which bond firmly to both the resin or metal of which the trays are constructed as well as the metal articulator frame. Among the many suitable bonding resins for this purpose are epoxy resins compositions containing amine, polyamide or other suitable hardeners; polymethylmethacrylic resin adhesives have provided good results. After the bonding resin has hardened, the jig 42 is removed and any flash is trimmed away; then the articulator is ready for use.

The completed articulator is illustrated in FIG. 2 with the conventional stop for restricting the closure of the device again omitted. The lower tray 24 is fastened to The trays 24 and 26 with their keyways 32 serve as molds for shaping the keys 62; and this casting operation isusually performed by the dental technician rather than the dentist. The dentist forwards the dental casting 58 along with the upper jaw casting and wax bite or impression (not shown). After assembling the two casts with the wax bite therebetween, the technician articulates this assembly visually in the articulator with the articulator turned onto its back so that its pivot pin 20 is now at the bottom; then he pours the plaster in the form of a paste or slurry to coverthe faces of the trays including the keyways 32 as well as the rough bases of the casts. Usually, the trays and keyways have previously been coated with a parting agent as described hereinafter. There is no embedding of the metal frame of the articulator as that member has already been permanently covered by the tray 24 and the bonding layer 52. Masking tape may be placed across the rear lips 28 of the trays to shield the back of the articulator pivot and chassis from unwanted plaster in this operation. When the plaster slurry has hardened and materials, such as polyethylene, it is usually preferred the lower platform 14 (see FIG. 1) is embedded and the to employ a parting agent before casting or molding coupling keys onto mounting bases for the-dental casts in order to insure easy separation of the undercut coupling keys and keyways. The parting agent is applied to the trays and their keyway slots but not to any part of the dental casts as the plaster should form firm bonds with those casts. Good results have been obtained with liquid silicone compositions, glycerine and hydrocarbon materials such as paraffin waxes, mineral oil and petroleum jelly.

These mounted casts are locked in place against any lateral (i.e., transverse) or vertical motion, but they can be simply and swiftly disengaged from the articulator by merely withdrawing them in a longitudinal direction, i.e., along the Freenum line. This prevents any breakage of casts resulting from turning the articulator on its side or top to examine the casts. Also, it is a simple matter to prevent accidental dislodgement in the longitudinal direction, as by merely fastening a piece of pressure-sensitive adhesive tape across the openings 34 at the front ends of slots 32. I

Although the keys and keyways may be aligned in a lateral direction, thereappears to be little or no advantage obtainable with such orientation; and there is probably greater likelihood of a cast accidentally slipping out of'the articulator and being broken when the dental casts are inspected at various angles.

While the aforesaid coupling members may be reversed in position so that the keyways are located in the mounting base 58, and also in the jig 42, while keys project from the operating faces of trays 24 and 26, little or no improvement appears to result from this configuration.

The present inventionprovides a number of significant advantages which result in substantial economies in both time and materials. For example,a dental technician can work more conveniently and rapidly on a dental restoration on a mounting base that has been removed from the articulator, as he is now able to work at any angle and from any side. In doing this, it is important that the technician is able to substantial instantaneously remove and replace the base without requiring rearticulation or realignment in the articulator in order to obtain that convenience in working. In the new system, the mounting bases align and lock in one motionas there is only one possible position of reengagement.

Less plaster is required because there is no need to embed the platform frame members therein. Also it is only necessary for the dental technician and the dentist to each have a single articulator of the improved model and this moderately heavy device does not have to be shipped back and forth, only the dental cast mounting bases must be sent. Moreover, the dentist and technician can employ entirely different types of articulator frames, even stem and pivot types, for work on the same dental restoration as long as the trays were fastened in place on the different articulators by using mounting jigs of the same dimensions. Also, the new articulator trays do not require the destruction of the casts in order to free them from the articulator frame. Accordingly, a patients casts can be kept indefinitely on the mounting bases along without the necessity of reserving an articulator exclusively for that particular patient. I

In addition, it was noted with considerable surprise that several badly chipped mounting base keys 62 provided precise alignment when the mounting bases were reinstalled in the articulator despite the badly battered condition of those coupling keys.

While the present invention has been described herein in respect to a limited number of embodiments for the purposes of a full disclosure, it will be readily apparent to those skilled in the art that many other modifications and variations are within the scope of this invention. Accordingly the present invention should not be considered as limited in any particulars except as may be recited in the appended claims or required by the prior art.

I claim:

1. In a dental articulator including a pair of opposed articulator platform members mounted to a frame structure in spaced relationship to one another, at least one of said platform members mounted for adjustable pivotal movement with respect to the other of said platfonn members, the improvement therein which comprises:

a tray member rigidly attached to each of said articulator platform members;

each of said tray members being provided with slidably engageable coupling means adapted to releasably lockably engage an article having a complementary shaped coupling means; said tray member coupling means having tapering dimensions in two different planes, said dimensions tapering in each plane in the direction of movement for coupling engagement between said tray member and said article.

2. An articulator as claimed in claim 1, wherein each of said tapering dimensions of said tray member coupling means tapers in a direction approaching the axis about which said articulator platforms are pivoted with respect to each other.

3. An articulator as claimed in claim 1, wherein each of said tray member coupling means comprises a longitudinally extending keyway slot having undercut side walls tapering toward each other in a direction approaching the pivotal axis of said articulator platform members, said undercut side walls of said keyway slot also tapering from top to bottom in said direction approaching said pivotal axis of said articulator platform members.

4. An articulator as claimed in claim 3, wherein said keyway slot has a substantially dovetail cross-section.

5. An articulator as claimed in claim 3, wherein the taper of said undercut side walls of said keyway slot toward each other is substantially greater than the taper from the top to the bottom of the slot.

6. An articulator as claimed in claim 5, wherein said undercut side walls of said keyway slot taper toward each other approximately from 860, and taper from top to bottom approximately at least 2.

7. An articulator as claimed in claim 6, wherein said undercut side walls of said keyway slot taper toward each other approximately 30.

8. In a combination of a dental articulator including a pair of opposed articulator platform members mounted to a frame structure in spaced relationship to one another, at least one of said platform members mounted for adjustable pivotal movement with respect to the other of said platform members, and a mounting base bearing a dental cast on one side thereof secured to each of said articulator platform members, the improvement therein which comprises:

a tray member rigidly attached to each of said articulator platform members;

each of said tray members provided with slidably engageable coupling means adapted to r'eleasably lockably engage complementary shaped coupling means provided on the underside of each of said dental cast mounting bases;

said tray member and dental east mounting base coupling means having tapering dimensions in two different planes, said dimensions tapering in each plane in the direction of movement for coupling engagement between said tray members and said mounting bases,

whereby said dental cast mounting bases are rapidly slid into precise locking engagement with said tray members on said articulator platform members.

9. The combination as claimed in claim 8, wherein each of said tray member coupling means comprises a longitudinally extending keyway slot having undercut side walls tapering toward each other in a direction approaching the pivotal axis of said articulator platform members, said undercut side walls of said keyway slot also tapering from top to bottom in said direction approaching said pivotal axis of said articulator platform members; and

each of said dental .cast mounting base coupling means comprises a longitudinally extending key member having a shape complementary to that of said keyway slot.

10. The combination as claimed in claim 9, wherein said key member and said keyway slot each have a substantially dovetail cross-section.

11. A' mounting jig for accurately aligning a pair of tray members in opposed registry and subsequent mounting to an associated pair of opposed platform members secured to a dental articulator frame'structure, comprising a block member having top and bottom faces spaced apart a distance corresponding to the distance of the opening between the articulator platform members; and

each of said top and bottom faces of the jig block having a longitudinally extending key member projecting outwardly therefrom, the longitudinally extending side edges of each of said key members being undercut and tapering both toward each other and from top to bottom from one end of said key member to the opposite end thereof. 1 12. A mounting jig as claimed in claim 11, wherein said top and bottom faces are spaced apart a distance of approximately 3.75-4.0 inches.

13. A mounting jig as claimed in claim 11, wherein said undercut side edges of each of said projecting keys taper toward each otherapproximately from 860 and taper from top to bottom approximately at least 2.

14. A mounting jig as claimed in claim 13, wherein said undercut side edges of each of said projecting keys taper toward each other approximately 30.

15. A method for positioning mounting bases bearing dental casts with repetitive accuracy on opposed platform members secured to a dental articulator frame structure, comprising the steps of:

forming a mounting jig having top and bottom faces spaced apart a distance corresponding to the distance of the opening between the opposed articulator platform members,

providing a longitudinally extending key member projection on each of said top and bottom faces of said jig block, and

undercutting the longitudinally extending side edges of each of said key members and tapering said side edges both toward each other and from top to bottom from one end of said key member to the opposite end thereof;

forming the underside of said mounting bases bearing dental casts with a key member identical to the shape of the key members formed on said mounting j g; sliding a tray member provided on one side with a keyway slot having a shape complementary to that of said key members formed on said jig block into releasable locking engagement with each of said key members on said top and bottom faces of said jig block; I

placing said mounting jig with said tray members releasably lockably engaged therewith between said opposed platform members of said dental articulator;

securing said tray members to said opposed platform members; and

thereafter slidably removing said mounting jig from said tray members secured to said opposed platform members of said dental articulator,

whereby said mounting bases bearing dental casts may be accurately repetitively positioned on said dental articulator by slidably engaging said tray membersaffixed to said opposed articulator platform members. 

1. In a dental articulator including a pair of opposed articulator platform members mounted to a frame structure in spaced relationship to one another, at least one of said platform members mounted for adjustable pivotal movement with respect to the other of said platform members, the improvement therein which comprises: a tray member rigidly attached to each of said articulator platform members; each of said tray members being provided with slidably engageable coupling means adapted to releasably lockably engage an article having a complementary shaped coupling means; said tray member coupling means having tapering dimensions in two different planes, said dimensions tapering in each plane in the direction of movement for coupling engagement between said tray member and said article.
 2. An articulator as claimed in claim 1, wherein each of said tapering dimensions of said tray member coupling means tapers in a direction approaching the axis about which said articulator platforms are pivoted with respect to each other.
 3. An articulator as claimed in claim 1, wherein each of said tray member coupling means comprises a longitudinally extending keyway slot having undercut side walls tapering toward each other in a direction approaching the pivotal axis of said articulator platform members, said undercut side walls of said keyway slot also tapering from top to bottom in said direction approaching said pivotal axis of said articulator platform members.
 4. An articulator as claimed in claim 3, wherein said keyway slot has a substantially dovetail cross-section.
 5. An articulator as claimed in claim 3, wherein the taper of said undercut side walls of said keyway slot toward each other is substantially greater than the taper from the top to the bottom of the slot.
 6. An articulator as claimed in claim 5, wherein said undercut side walls of said keyway slot taper toward each other approximately from 8*-60*, and taper from top to bottom approximately at least 2*.
 7. An articulator as claimed in claim 6, wherein said undercut side walls of said keyway slot taper toward each other approximately 30*.
 8. In a combination of a dental articulator including a pair of opposed articulator platform members mounted to a frame structure in spaced relationship to one another, at least one of said platform members mounted for adjustable pivotal movement with respect to the other of said platform members, and a mounting base bearing a dental cast on one side thereof secured to each of said articulator platform members, the improvement therein which comprises: a tray member rigidly attached to each of said articulator platform members; each of said tray members provided with slidably engageable coupling means adapted to releasably lockably engage complementary shaped coupling means provided on the underside of each of said dental cast mounting bases; said tray member and dental cast mounting base coupling means having tapering dimensions in two different planes, said dimensions tapering in each plane in the direction of movement for coupling engagement between said tray members and said mounting bases, whereby said dental cast mounting bases are rapidly slid into precise locking engagement with said tray members on said articulator platform members.
 9. The combination as claimed in claim 8, wherein each of said tray member coupling means comprises a longitudinally extending keyway slot having undercut side walls tapering toward each other in a direction approaching the pivotal axis of said articulator platform members, said undercut side walls of said keyway slot also tapering from top to bottom in said direction approaching said pivotal axis of said articulator platform members; and each of said dental cast mounting base coupling means comprises a longitudinally extending key member having a shape complementary to that of said keyway slot.
 10. The combination as claimed in claim 9, wherein said key member and said keyway slot each have a substantially dovetail cross-section.
 11. A mounting jig for accurately aligning a pair of tray members in opposed registry and subsequent mounting to an associated pair of opposed platform members secured to a dental articulator frame structure, comprising a block member having top and bottom faces spaced apart a distance corresponding to the distance of the opening between the articulator platform members; and each of said top and bottom faces of the jig block having a longitudinally extending key member projecting outwardly therefrom, the longitudinally extending side edges of each of said key members being undercut and tapering both toward each other and from top to bottom from one end of said key member to the opposite end thereof.
 12. A mounting jig as claimed in claim 11, wherein said top and bottom faces are spaced apart a distance of approximately 3.75-4.0 inches.
 13. A mounting jig as claimed in claim 11, wherein said undercut side edges of each of said projecting keys taper toward each other approximately from 8*-60* and taper from top to bottom approximately at least 2*.
 14. A mounting jig as claimed in claim 13, wherein said undercut side edges of each of said projecting keys taper toward each other approximately 30*.
 15. A method for positioning mounting bases bearing dental casts with repetitive accuracy on opposed platform members secured to a dental articulator frame structure, comprising the steps of: forming a mounting jig having top and bottom faces spaced apart a distance corresponding to the distance of the opening between the opposed articulator platform members, providing a longitudinally extending key member projection on each of said top and bottom faces of said jig block, and undercutting the longitudinally extending side edges of each of said key members and tapering said side edges both toward each other and from top to bottom from one end of said key member to the opposite end thereof; forming the underside of said mounting bases bearing dental casts with a key member identical to the shape of the keY members formed on said mounting jig; sliding a tray member provided on one side with a keyway slot having a shape complementary to that of said key members formed on said jig block into releasable locking engagement with each of said key members on said top and bottom faces of said jig block; placing said mounting jig with said tray members releasably lockably engaged therewith between said opposed platform members of said dental articulator; securing said tray members to said opposed platform members; and thereafter slidably removing said mounting jig from said tray members secured to said opposed platform members of said dental articulator, whereby said mounting bases bearing dental casts may be accurately repetitively positioned on said dental articulator by slidably engaging said tray members affixed to said opposed articulator platform members. 